Hi,
I am new to RC. I just bought a toy rc plane with a 3.7V 200Mah LiPo battery. I didnt know about not completely discharging the battery and hence battery was dead in two days.
I then bought a replacement 3.7V 500Mah battery but unfortunately connectors in the two battery are incompatible. I am attaching the photos of the two connectors.

Please help.

Are you sure your plane can handle the weight of the 500 mah battery?

If not then do not do what I am about to tell you

Cut the wires on both lipo (ber very careful not to get the wire touch each other) and just replace the connectors of the battery making sure you have the correct polarity.